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17-4PH shiny or not

I can have it both ways but which is correct. I have had 17-4Ph passivated and have had it returned with the same light brownish color that it came back from the heat treaters with. I asked the Plater and he said that they had did it wrong and he could fix it and gave it back next time shiny bright. I have recently been given parts by a subcontractor and the parts have varied in shades from blackish and other parts shades of reddish purple. None of these were shiny bright (silver in color). Yet He supplied me with heat treat and passivation certs. What is one to expect? these parts are medical in nature. Seems they should be shiny bright. What is the standard who knows what is going on here and has the definitive answers?

TY

Gordon Web
passivating 17-4PH - San Jose, California, USA
2004

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2004

Passivation specifications require removal of any heat treat scale (e.g., Paragraph 3.2 of QQ-P-35C (canceled) [link is to free spec at Defense Logistics Agency, dla.mil]C). Parts possessing heat treat scale should not be certified as having been properly passivated. Scale is difficult to sterilize in comparison to the very thin, ~amorphous oxide formed by passivation. Ask your subcontractor for liability insurance coverage.

Passivation only maintains the shine present after any descaling. "Shiny bright" is a requirement for the heat treater. For parts final machined prior to heat treatment, it is far better to avoid oxidation (inert gas, vacuum, protective coatings, wrapping in stainless foil, etc.) than to descale afterwards. Descaling removes material and (except for electropolishing) dulls the finish. Acid pickling may cause hydrogen embrittlement and intergranular attack. Small traces of heat tint may be removed by either a brief electropolishing or a closely watched dip of up to 2 minutes in a 10:1 nitric acid-HF solution (seems that your plater knows this).

Ken Vlach [deceased]
- Goleta, California
Finishing.com honored Ken for his countless carefully researched responses. He passed away May 14, 2015.
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